Synchronised system for the production of crude oil by means of in-situ combustion

ABSTRACT

A synchronized crude oil production system using in-situ combustion that measures, monitors, and controls the operating conditions in real time. The system includes at least one injection well, at least one production well, and at least one inclined synchronization well. The end of the production well(s) and the end of the inclined synchronization well(s) within the reservoir are oriented outward the injection well and the wells include measurement, monitoring, and control elements. The measurement and monitoring elements transmit signals and data collected to one or more processing units which, together or independently, use an analytical model to assess the combustion conditions in the well-subsurface system and the forward move of the combustion front and, depending on the results, synchronize the production operations. Each well being operated and handled remotely at the control valves thereof in order to influence the displacement direction of the combustion front.

The invention relates to a synchronized crude oil production system using in-situ combustion. The system measures, monitors and controls the operating conditions in real time and comprises at least one injection well (1), at least one production well (2) and at least one inclined synchronization well (3). According to the invention, the end of at least one production well (2) and the end of at least one inclined synchronization well (3) are oriented outward the injection well (1). In addition, the system comprises measurement, monitoring and control elements that transmit signals and information detected thereby to one or more processing units which, together or independently, use an analytical model to assess the combustion conditions and the advance of the combustion front and, depending on the results, synchronize the production operations, each well being operated and handled remotely at the control valves thereof in order to influence the displacement of the combustion front.

BACKGROUND

Heavy crude oil or extra heavy crude oil is any type of high-density crude oil which does not flow easily. It is referred to as “heavy” because its density or API gravity is less than 21.9° API.

The largest reserves of heavy crude oil in the world are located north of the Orinoco River in Venezuela, but 30 or more countries are known to have reserves. Canada has large heavy crude oil reserves, mainly in the provinces of Alberta and Saskatchewan. In this sense, in the last decades, specialized techniques have been developed for the efficient and economical production of such deposits.

Production, of heavy and extra heavy crude oil present special challenges compared to light crude oil due to their high viscosity, and consequently low mobility and low API gravity.

To overcome such challenges, several Thermal Recovery methods have been developed. Among such methods, there are different types of steam injection techniques such as Steam Assisted Gravity Drainage (SAGD). This technique involves the use of two horizontal wells instead of vertical wells, wherein the operators inject high temperature steam into the upper wellbore, the steam flows through the well, heats the oil by heat transfer and reduces its viscosity, causing the heated oil to drain into the lower horizontal wellbore. According to literature available, SAGD has an estimated recovery rate of 20%-50% of in situ oil, however, the implementation rate is limited to a type of oil reservoirs, mostly those not affected by strong aquifers and with an excellent vertical communication.

Another broadly used method, with a greater implementation range, is in situ combustion. Such method involves heating and oxidizing a small amount of oil existing within the reservoir in order to generate thermal energy. Such energy allows displacement of a considerable oil bank from the injection wells to production wells mostly due to the viscosity reduced, vaporization and carry forward of the gases formed in the combustion process. Although this type of process has existed for a long time, there have been technical-operating difficulties discouraging its application, such as the control and monitoring of the combustion front, which directly affects the volumetric sweep efficiency and, therefore, the recovery of the oil existing gin the reservoir. However, there have been efforts to overcome such difficulties which have reached reservoir recovery over 60%, as reported in several bibliographic sources and pilot and commercial projects carried out around the world. Heavy crude oil reservoirs subjected to hydraulic pressure respond favorably to this type of method.

Generally, three chemical processes take place in an in situ combustion: Oxidation: The combustion zone acts like a piston displacing the fluids in the combustion front to the production wells. Coking: Oxygen combines with oil resulting in carbon dioxide and heat. The combustion reaction is maintained by injecting air, and the CO₂ released in the reservoir produces a decrease of the relative permeability to water, which minimizes the water mobility respecting oil.

Cracking: The thermal cracking creates a coke deposit in the fire front generating, in some cases, an improvement of the crude oil, combustion gases vaporize the water, improve the displacement of fluids and increase the sweep efficiency of the process. In summary, the in situ combustion process has a number of advantages, mainly in reservoirs with high water saturation or direct influence of aquifers with strong hydraulic drive: improvement of the crude oil vs. water mobility ratio by reducing the relative permeability to water, positive influence on the gravitational segregation by creating a secondary high pressure gas layer and reduction of crude oil viscosity by heating and miscibility of CO₂ produced. In addition, the saturation of residual oil is reduced and saturation of irreducible water increases due to the temperature increase as reported in the oil industry literature, which increases the oil flow and decreases the water flow.

Given the significant increase of heavy and extra-heavy crude oil reserves worldwide, the search of technologies optimizing the above-mentioned technologies has been a concern in the world oil industry. In particular, there is a need for a production method monitoring and controlling the specific operations existing in an in situ combustion, thereby increasing the hydrocarbon production and reserves, meaning the amount of oil recoverable from the reservoir in cost-effective conditions.

In this sense, the main purpose of the present invention is to provide a synchronized crude oil production system using in-situ combustion, comprising real time measurement, monitoring and control elements for the combustion front and further comprising a geometry and type of well that make easier and more efficient the management of monitoring and control operations of such combustion front.

Another purpose of the present invention is to provide a synchronized crude oil production system using in-situ combustion comprising a type of well referred to as inclined “synchronization” well, also equipped with measurement and monitoring elements, that may fulfill different functions within the system making more efficient the control operations in the combustion front. The main purpose of the inclined synchronization wells (3) is not only to produce a higher volume of hydrocarbons, but to complement the measurement, monitoring and control of the combustion front in order to make the process for efficient and achieve a greater hydrocarbon recovery. There is a significant economic justification regarding inclined wells. An inclined well is much more economical and easier to drill than a horizontal well, although it has its advantages due to its larger flow area. Its geometry or architecture does not require the use of sophisticated drilling equipment like horizontal wells, where it is necessary to “sail” through sometime very low-density sands that make difficult its trajectory. Such “Measurement While Drilling” (“MWD”) tools are very expensive and put up the cost of the well. In field with large volumes of reserves and where it is convenient to implement in situ combustion processes requiring to drill economical wells the cost of wells is extremely important, representing over 60% of the overall cost of the investments in to project. This is why it is important to count on inclined, synchronized wells located at the reservoir, allowing to monitor and control the combustion front and to maintain and improve the volumetric sweep efficiency, maximizing the oil reserve recovery.

DESCRIPTION OF THE INVENTION Description of the Figures

FIG. 1 is a drawing of a prior art arrangement for crude oil recovery from a reservoir by in situ combustion showing the two main zones of the well-subsurface system and the combustion front displacing from the injection well 1 to the horizontal production well 2, combustion zone C and a zone adjacent to the combustion front, the non-combustion zone D.

FIG. 2 is an upper view of a prior art arrangement for crude oil recovery showing an ideal theoretical displacement of the combustion front of the well-subsurface system from an injection well 1 to vertical production wells 2. The arrows in this figure show the direction of the combustion front.

FIG. 3 is an upper view of an arrangement for crude oil recovery from a reservoir showing one of many theoretical forms that a combustion front in the well-subsurface system might have due to the irregular displacement of the crude oil. This figure intends to show that in real life, the combustion front is not homogeneous, which certainly affects the productivity of the process, the volumetric sweep efficiency and accordingly the hydrocarbon reserve recovery. In this figure, the arrows show the direction of the combustion front.

FIG. 4 a is an upper view of an arrangement for crude oil recovery from a well-subsurface system according to a first embodiment of the invention with inclined production wells at instant t₁ (referential), showing an irregular combustion front under undesired conditions without applying Synchronized Operations Management “SOM” to monitor and control the combustion front and improve the sweep or displacement efficiency and the hydrocarbon reserve recovery. In this figure, the arrows show the direction of the combustion front.

FIG. 4 b is an upper view of an arrangement for crude oil recovery from a well-subsurface system according to the embodiment of FIG. 4 a at instant t₂ (referential and subsequent to t₁) showing a uniform, optimal combustion front under desired operating conditions, after the synchronization operations by monitoring and control of the invention. In this case, synchronized operations management concepts have been applied for measuring, monitoring and controlling the combustion front. In this figure, the arrows show the direction of the combustion front.

FIG. 5 is an interior side view of zone X of FIG. 4 b, showing the relative position among injection wells, inclined production wells and synchronization wells, highlighting a first embodiment of the invention with inclined synchronization wells and production wells.

FIG. 6 is an upper view of an arrangement for crude oil recovery from a well-subsurface system according to a second embodiment of the invention using multilateral production wells and inclined synchronization wells strategically located. Such configuration of multilateral production wells and inclined synchronization wells represents an optional embodiment of the invention. Note that the direction of the multilateral section of production wells and inclined synchronization wells is outward. In this figure, the arrows show the direction of the combustion front.

FIG. 7 is an interior side view of zone X of FIG. 6 showing the relative position among the injection well, the multilateral wells and the inclined synchronization wells highlighting an optional embodiment of the invention.

FIG. 8 is an upper view of an arrangement for crude oil recovery from a well-subsurface system according to an optional embodiment of the invention showing a uniform, optimal combustion front under desired operating conditions after the synchronization operations by monitoring and control of the invention. In this figure, the arrows show the direction of the combustion front.

FIG. 9 is a map representing a referential reservoir used for a simulation of an arrangement according to FIG. 6 of the invention showing several layers, oil sands from which oil is recovered and the last layer represents an aquifer or water zone which is the main source of water.

FIG. 10 is a chart representing the production data from synchronization wells (3 a), (3 b), (3 c) and (3 d) according to FIG. 9 in barrels per day as a function of time obtained by simulation. Such wells are normally useful to support production wells in crude oil recovery.

FIG. 11 is a chart representing the estimate production of barrels per day as a function of time for multilateral wells 2 a, 2 b, 2 c and 3 d resulting from a referential simulation.

DESCRIPTION

The present invention provides a synchronized arrangement of wells in an oil reservoir for measuring, monitoring and controlling in situ combustion front parameters to achieve a more efficient hydrocarbon recovery from the well-subsurface system. In order for the in situ combustion recovery process to be efficient, mainly in reservoirs with high hydraulic pressure, it is necessary to improve the water/oil mobility ratio due to the decrease of the relative water permeability respecting oil and due to the heat created in the reservoir, taking advantage of the positive effects of the miscibility of CO₂ in crude oil. The result is an enhanced efficiency of displacement or volumetric sweep and, therefore, a greater hydrocarbon reserves recovery.

Thermal processes and kinetic reactions taking place in an in situ combustion process are the typical ones. On the one hand, there will be a heat oil front in the combustion zone C (see FIG. 1) that will result in an oil viscosity decrease and, therefore, will increase mobility respecting water, making easier the entrance of oil into the closest production well (2). Regarding the crude oil located in the non-combustion zone D or zone not affected directly by the combustion front (see FIG. 1), the heat transferred will also have a positive effect in reducing the crude oil viscosity, resulting in an improved oil mobility thus increasing the probability of more hydrocarbon reserves recovery.

Another beneficial aspect is the flowing of combustion byproduct gases to higher zones of the sand structure or the upper zone of the reservoir. The combined effect of the heat transfer, the oil viscosity reduction and gravitational segregation resulting from the formation of a secondary gas layer at a higher pressure makes the oil flow downwards thereby enhancing the sweep efficiency, increasing the oil displacement and thus increasing the hydrocarbon reserves recovery.

FIG. 2 shows a prior art combustion crude oil recovery system showing comprising an arrangement of 5 inverted wells, which for referential purposes include a vertical injection well (1) and four vertical production wells (2). In this figure, the injection well (1) is located within the arrangement within the area defined by the production wells (2). The function of the injection well (1) is to provide air, oxygen or a mixture of oxidizing gases to displace the crude oil within its influence area and maintain the combustion reaction in the reservoir. Zone (A) represents the limits of the combustion front within the reservoir and the arrows thereon represent the same theoretical direction of the front as it goes forward to reach the production wells (2) and thus recover the oil from the reservoir. In real life, the combustion front does not travel homogeneously, and therefore, as time goes by, the form of zone A departs from symmetry. FIG. 3 shows a referential example of a combustion crude oil recovery system wherein zone B represents a combustion zone near reality, when no measures to control it are taken. As shown, the combustion front in amorphous and thus the oil in the vicinity of the production well (2 c) cannot be recovered from the reservoir, affecting significantly the productivity of production wells, the volumetric sweep efficiency and the hydrocarbons reserves recovery. This reality may be corrected by including a greater number of production wells (2) within the arrangement each including, in turn, monitoring and controlling tools for the combustion reactions and the forward move of the combustion front so as to control the direction desired. However, such addition of production wells (2) involves additional costs in well drilling and completion operations which are useless once the combustion front (zone B) has passed through the area underneath such wells.

DETAILED DESCRIPTION OF THE INVENTION

The synchronized crude oil production system using the in situ combustion process of the present invention provides: including measurement, monitoring and control elements in the vertical injection wells (1), production wells (2) present in a well arrangement, and further introducing a new type of well referred to as inclined “synchronization well” (3), including, in turn, measurement elements for pressure and temperature, among other variables, at different levels of the well, and monitoring and control elements for the gases created from the combustion front. A system according to the invention comprises at least one injection well (1), at least one production well (2) and at least one synchronization well (3). FIGS. 4 a and 4 b include for referential purposes at least four inclined synchronization wells (3) in an arrangement comprising one injection well (1) and four inclined production wells (2).

The term “inclined” used in reference to certain wells should be understood so that the inclination of the well may go from the surface to one end thereof or comprise a vertical section and an inclined section, where the inclined section is in contrast with a substantially horizontal or substantially vertical section. In this sense, an inclined production well (2) and an inclined synchronization well (3) of the present invention does not include a horizontal well configuration such as that of the prior art, which include a substantially vertical section and a substantially horizontal section attached thereto.

As mentioned above, each injection (1), productions (2) and synchronization (3) well has measurement, monitoring and control elements for the combustion front (zone B), being such elements related to the functions of each well within the arrangement. Generally air, oxidizing gas, a mixture of oxidizing gases and other fluids are injected through the injection well (1) in order to displace the crude oil and maintain the combustion reaction to the production (2) and synchronization (3) wells more efficiently. Regarding new production wells that may exist in the field (2), they will fulfill a double function: first, such wells will serve to produce the crude oil displaced by the combustion front (combustion zone) and adjacent zones (zones influenced indirectly by heat transfer), including the crude oil displaced by gravitational segregation. Second, production wells (2) will serve as monitoring wells for the combustion conditions in the well-subsurface system. Inclined synchronization wells (3), duly equipped with remote pressure and temperature sensors, will have, among others, several functions. First, they serve as a support for production wells (2) for measuring, monitoring and controlling the combustion front by synchronized operations management; second, they will serve as additional production wells, and third, they may serve as wells for the release of undesired gases from the well-subsurface system, when required. Finally, such inclined synchronization wells (3) may be converted into oxidizing gas injection wells, if it is so required and permitted by the conditions of the process. Their construction is carried out so that such function is feasible technically (see FIGS. 5 and 7).

Among the measurement and monitoring equipment to be installed there are remote pressure and temperature sensors operating in real time, however, there may be other combustion front control elements, such as 4D seismic data recovery, flow logs and imaging equipment installed in some or all of the wells. Such measurement and monitoring elements send the signals and data collected by them to a processing unit in charge of evaluating the combustion conditions of the well-subsurface system and the forward move of the combustion front. If the data collected in each type of well is within the desired operating conditions, the injection (1), production (2) and inclined synchronized (3) wells will continue with their basic functions within the arrangement. On the contrary, if the data collected show that a zone is being affected adversely or preferentially by the combustion process to an undesired direction, “Synchronized Operations Management”, “SOM”, consisting in synchronizing the production operations so that each well or group of wells is handled remotely in its control valves to influence the displacement direction of the combustion front and make it uniform. For example, if at certain moment the combustion front goes preferentially or prematurely towards certain direction, a temperature or pressure profile change will be detected at any inclined synchronization well (3) or production well (2), these changes being immediately registered in the data processing unit, where the operators may issue instructions in real time to any or all inclined synchronization wells (3) or production wells (2). Such instructions consist in the synchronized and remote management of the production control valves of the wells, causing the modification of the production pattern and accordingly the forward move of the combustion front, redirecting it towards the direction desired. The operator may even send instructions to the injection well in order to decrease, increase or regulate the amount of oxidizing gas being injected into the well-subsurface system.

Instruction may be also given for the complete shutdown of wells, including the activation of water injection systems to control any abnormal situation taking place in any well or the reservoir itself.

Another alternative is that inclined synchronization wells (3) may act as release wells or valves in case that gas concentration within the reservoir exceeds permitted values; in such case, the control unit can send an instruction to activate the release or gas extraction function.

The number and geometry of the injection well (1), production well (2) and inclined synchronization well (3) in the arrangement of the system of the present invention will depend on the type of reservoir, the type of arrangement and the exploitation conditions of the reservoir. Injection (1), production (2) and inclined synchronization (3) wells are in a particular geometric arrangement according to the requirements of the well-subsurface system to be produced.

Each well of the arrangement of FIGS. 4 a and 4 b, whether injection wells (1), inclined production wells (2) or inclined synchronization wells (3), will be connected to one or several processing units jointly or independently. In any connection configuration, the processing unit is capable of interpreting the measurements from every well and sending the signals in order for the operator take the necessary correctives. Therefore, the invention provides an intelligent measurement, monitoring and control system which steps comprise evaluating in real time and constantly the conditions of in situ combustion reaction in the well-subsurface system (at different interest points duly identified), sending of signals to the processing unit, analyzing independent evaluations from each of the wells and, based on the results, determining automatically by software or computing model the correctives necessary to uniform the combustion front.

PREFERRED EMBODIMENTS OF THE INVENTION

In a first preferred embodiment of the invention, the injection wells (1) are vertical, the production wells (2) are inclined and synchronization wells (3) are inclined as shown in FIG. 5. Such configuration allows a better coverage of the area of the well-subsurface system to be produced, making more efficient the monitoring process and accordingly the production process. The use of vertical production wells generally has the restriction that its function is limited to a single point of the well and/or subjacent area thereof. On the contrary, this preferred embodiment of the invention involves the use of vertical injection wells (1) and inclined production wells (2), so as to access to a specific region considered as relevant in the well-subsurface system. Regarding synchronization wells (3), strategically located within the arrangement of the invention, their configuration is inclined, permitting a better position with a greater flow area and orientation towards the points into the well-subsurface system considered as relevant for monitoring purposes.

In a second preferred embodiment of the invention, injection wells (1) are vertical, production wells (2) are multilateral, and synchronization wells (3) are inclined as shown in FIGS. 6 and 7. This configuration allows a greater coverture of the well-subsurface area to be produced, making more efficient the monitoring process and accordingly, the production process. Such preferred embodiment involves the use of vertical injection wells (1) and multilateral production wells (2) so as to cover a greater area of the well-subsurface system. Regarding the inclined synchronization wells (3), they are strategically located within the arrangement of the invention, their configuration is always inclined, which allows a better position with a greater flow area and orientation towards the points into the well-subsurface system considered as relevant for monitoring purposes.

For the two preferred embodiments described above, the relative position of the inclined synchronization wells (3) in the arrangement is relatively close to the production well (2) and, if more than one production wells (2), preferably the zone adjacent to the two closest production wells (2). Preferably, however, the synchronization wells (3) shall be close to an intermediate and strategic position from the geological point of view to the injection well and the production wells (2), and placed within the zone Z (shown in FIGS. 4 a, 4 b, 5, 6, 7 and 8).

Regarding the production wells (2) and inclined synchronization wells (3) they are oriented so that the end of the production wells (2) and the end of the inclined synchronization wells (3) within the reservoir is outward respecting the injection well (1). Generally, production wells (2) have a single inclined or multilateral portion. However, they may have a substantially vertical section and/or one or more inclined sections, which make them multilateral. The number of production wells (2) and inclined synchronization wells (3) may vary depending on the features of the reservoir and the location of existing wells in the field at the beginning of the in situ combustion process. Such preferred embodiments and relative arrangements of the injection wells (1), production wells (2) and inclined synchronization wells (3) to carry out the invention are shown in FIGS. 4 a, 4 b, 5, 6, 7, and 8.

EXAMPLE (NUMERICAL SIMULATION)

With the purpose of evidencing the advantages of the invention, a numerical simulation was carried out by using the STARS numerical simulator by CMG in one of the fields of Pacific Rubiales Energy. STARS include the multiphasic flow of oil, water and gas, the heat transfer, compositional changes and chemical, physical and kinetic reactions taking place in the reservoir during in situ combustion. In order to evaluate the behavior of the reservoir subjected to in situ combustion using different well arrangements and in this case combination of injection wells (1), multilateral production wells (2) and inclined synchronization wells (3), an historical comparison of the production of production wells existing in the field was carried out and the typical kinetic reactions of the process were applied, among other reservoir and design variables, such as: Four inclined synchronization wells (3) four multilateral production wells (2), one vertical injection well (1) injecting constantly 2.5 million cubic feet of air per day during 5 years in an area of 25 acres in a crude oil reservoir of more than 2,800 feet in depth.

The spacing and location of wells may be seen in FIG. 9, showing an schematic view of the reservoir, where simulations where carried out in order to determine the behavior of the production for each of the wells involved and the hydrocarbon reserves that may be recovered by using the process and well arrangement described. Such spacing and location of the wells is related to the arrangement shown in FIG. 6. The reservoir section selected in shown in FIG. 9.

Results of Numerical Simulations

The results of numerical simulations are summarized as follows:

The estimated production of the inclined synchronization wells (3) used in the simulation is shown in FIG. 10. The production of vertical wells was higher than 1,000 BPD at the beginning and it was maintained for a reasonable time period as a consequence of the in situ combustion process using the synchronization technique explained in previous chapters.

Likewise, FIG. 11, shows the oil production of “outward” multilateral production wells 2 a, 2 b, 2 c and 2 d in the selected sector. Such wells began with production rates higher than 3,000 BPD and were maintained over 1,000 BPD.

The foregoing behavior and the one of synchronization wells allow concluding that the proposed well arrangement is successful in increasing the volumetric sweep efficiency and accordingly the recovery of hydrocarbon reserves in over 40% of the oil originally on site.

The description of the present invention is referential, so it must be understood broadly. Also, figures and examples are for reference purposes to assist in understanding the principles and contributions of the invention to the prior art and shall not be understood as exhaustive and/or exclusive. 

1. A synchronized crude oil production system using in-situ combustion that measures, monitors, and controls operating conditions in real time, the system comprising: an injection well; a production well; and an inclined synchronization well, wherein an end of the production well and an end of the inclined synchronization well within a reservoir are oriented outward with respect to the injection well, wherein the injection, production, and inclined synchronization wells include a plurality of measurement, monitoring, and control elements, wherein the plurality of measurement and monitoring elements transmit signals and data collected thereby to one or more processing units, wherein the one or more processing units, together or independently, use an analytical model to assess combustion conditions in a well-subsurface system and a forward move of a combustion front and synchronize production operations, wherein each well is configured to be operated and handled remotely at control valves thereof in order to influence a displacement direction of the combustion front.
 2. The system according to claim 1, wherein the production well is inclined.
 3. The system according to claim 1, wherein the production wells is multilateral.
 4. The system according to claim 1, wherein the injection well, the production well, and the inclined synchronization well are in a particular geometrical arrangement according to requirements of the well-subsurface system to be produced.
 5. The system according to claim 1, wherein the inclined synchronization wells is in a relative position within the arrangement that is relatively closer to the production well than to the injection well.
 6. The system according to claim 1, wherein the inclined synchronization well is located within the zone Z between the production well and the injection well.
 7. The system according to claim 2, wherein the injection well, the production well, and the inclined synchronization well are in a particular geometrical arrangement according to requirements of the well-subsurface system to be produced.
 8. The system according to claim 3, wherein the injection well, the production well, and the inclined synchronization well are in a particular geometrical arrangement according to requirements of the well-subsurface system to be produced.
 9. The system according to claim 2, wherein the inclined synchronization well is in a relative position within the arrangement that is relatively closer to the production well than to the injection well.
 10. The system according to claim 3, wherein the inclined synchronization well is in a relative position within the arrangement that is relatively closer to the production well than to the injection well.
 11. The system according to claim 4, wherein the inclined synchronization well is in a relative position within the arrangement that is relatively closer to the production well than to the injection well.
 12. The system according to claim 2, wherein the inclined synchronization well is located within the zone Z between the production well and the injection well.
 13. The system according to claim 3, wherein the inclined synchronization well is located within the zone Z between the production well and the injection well.
 14. The system according to claim 4, wherein the inclined synchronization well is located within the zone Z between the production well and the injection well.
 15. The system according to claim 5, wherein the inclined synchronization well is located within the zone Z between the production well and the injection well. 